This invention relates to novel non-linear optical material and non-linear optical devices which are essential for an optical signal processing system involving, for instance, such operations as optical parametric oscillation, harmonic generation and optical switching.
Non-linear optical material, which is expected to play an important role in the art of optical communication, is capable of performing multiple functions such as optical mixing, parametric oscillation, harmonic generation and optical switching owing to the non-linear optical response of the material. Hitherto, crystals of such inorganic substances as KH.sub.2 PO.sub.4, NH.sub.4 H.sub.2 PO.sub.4 and the like have been used as said non-linear optical material. These substances, however, are still unable to meet the requirements for said uses because of their low non-linear susceptibility, deliquescency and low damage threshold value.
Ever since clarification of excellent properties of organic non-linear optical materials making use of .pi. electron polarization by disclosure of the facts that said organic non-linear optical materials have a greater non-linear optical coefficient than the inorganic materials, have generally no deliquescency and are high in damage threshold value, the extensive studies and development have been made on organic non-linear optical materials in many fields of science. The results of the latest studies are given in detail in, for instance, D. S. Chemla and J. Zyss: Nonlinear Optical Properties of Organic Molecules and Crystals, Vols. 1 and 2, Academic Press, 1987.
Neverthless, there is yet available no material having a large enough non-linear optical coefficient to enable attainment of the object with use of low-power laser such as semiconductor laser, and thus development of novel material capable of meeting said requirements has been strongly desired.